The present invention is relative to drilling rigs and, in particular, it is relative to a mobile drilling rig of the electric-hydraulic type comprising a telescopic mast and a mobile drill pipe storing and handling system.
In particular, the drilling rig according to the present invention can be associated with a vehicle for the transportation of the drilling rig itself.
Drilling rigs are known, which are associated with a vehicle for the transportation of the drilling rig itself.
These vehicles can be trucks, trailers or semi-trailers.
Said drilling rigs comprise a mast and a carriage that slides on the mast, along suitable guides, and supports the drilling head.
During the transportation, said mast is closed and arranged horizontally on said transportation vehicle.
Said mast is raised, in the working configuration, which is arranged vertically relative to the ground, by means of hydraulic pistons and mechanical systems that are known to a skilled person.
The technical features required for the drilling, in order to reduce the trip-in time and the trip-out time of a drilling system, lead the constructors of said drilling rigs to manufacture drilling rigs that allow users to use a drill string that is as long as possible. Normally, this technical feature forces constructors to manufacture drilling rigs with large dimensions.
This manufacturing feature generates a technical problem concerning the transportation of a structure with remarkable dimensions, both in terms of weight and size and in terms of ability to actually maneuver the vehicle on which the mast and the other elements of the drilling rigs are arranged.
Furthermore, every single country has its own laws regulating the dimensions and the maximum weight of the vehicles for the transportation on wheels, thus causing the movement of the drilling rigs from one drilling area to the other to become even more difficult.
The European patent no. EP0548900 describes a mobile drilling rig comprising a telescopic mast, which can be extended by means of a central hydraulic cylinder.
Another problem arising from the increase in the dimensions and the weigh of the drilling rig and, in particular, of the mast is relative to the forces acting upon the mast. As a matter of fact, structures with large dimensions produce an increase in the compression force acting upon the mast, which is transferred, through the drill floor, to the base section.
The structure of the mast, which is adapted to control the movements of the carriage comprising the drilling head, must be able to counter the torsion transmitted to the drill string by the drilling head itself.
Furthermore, the great length of the mast can cause a bending moment, which is generated by the lack of symmetry of the compression forces relative to the longitudinal axis of the mast.
In order to solve the latter problem and avoid damages to the structure of the mast, constructors increase the dimensions of the mast even more, so as to strengthen the structure of the mast itself. The greater sturdiness of the mast, though, worsens the technical problem concerning the increase in the mass of the drilling rig.
The increase in the overall mass and dimensions of the drilling rig leads to an increase in the costs for the installation and the removal of the drilling rig itself.
Furthermore, as already mentioned above, the increase in the mass of the drilling rig and, in particular, of the mast causes an increase in the compression force, thus forcing manufacturers to also strengthen the drill floor and the base section in order to correctly unload said compression force.
Designing technical features are aimed at providing a main load carrying member that is contained in the structure or skeleton of the mast, but is distinct from the mast. Furthermore, designing technical features require the loads acting upon said element to be perfectly symmetrical, so that the compression is entirely unloaded onto said element and the mast is not subject to the bending moments.
In the state of the art these objects cannot be reached, since the continuous movement of the drilling head, performed by lengthening and shortening the length of the mast itself, causes bending moments to the structure of the mast. These bending moments are normally countered by strengthening the structure and, hence, by increasing the weight of the drilling rig with the problems mentioned above.
In the prior art, as described for example in patent EP 0548900B1, the drilling head is caused to move up and down by hydraulic devices, such as hydraulic cylinders and hydraulic motors. The use of a hydraulic raising system reduces the energetic efficiency of the drilling rig. As a matter of fact, in order to actuate the hydraulic devices, the electric motors must actuate hydraulic pumps, with a first transformation from electric energy into fluidic energy. These pumps feed hydraulic devices, such as hydraulic cylinders or motors, thus performing a second transformation from fluidic energy into mechanical energy, with the consequent reduction of the efficiency of the system.